1. Field of the Invention
The invention relates to a filter bag for a filter device, said filter bag comprising a tubular, flexible, air-penetrable filter body provided with a suspension arrangement at an unfolded end thereof, said suspension arrangement comprising a rigid ring element annularly secured to said unfolded end of the filter body. The invention also relates to a filter device comprising a housing with a dust chamber and a clean-air chamber that are separated by an partition wall suspending at least one filter bag that extends through an opening provided in the partition wall with a main part of the filter body located in the dust chamber.
2. The Prior Art
Conventionally, a filter bag with a tubular, flexible, air-penetrable filter body made of e.g. felt has an upper end that is folded about an annular ring consisting of a metal ring and two axially spaced apart bead rings with a layer of filter material between the metal ring and the two bead rings as shown in FIG. 1. The back-folded end of the filter body is sewn to the main part of the filter body below the annular ring. The filter body material between the two bead rings forms a sealing between the filter bag and the partition wall, when the filter bag is mounted in a filter device. These types of filter bags are used in filter devices with CIP (cleaning-in-place) means as well as in filter devices without CIP means. A disadvantage of this type of filter bag is that it is difficult to clean, since the folded end of the filter bag creates a pocket containing the metal ring and the two bead rings. First, the metal ring and the two bead rings are difficult to clean since they are located in the pocket. Second, any undesired material resting inside the pocket—it being particles that have being sewn in during manufacturing of the filter bag or product material that has penetrated through the filter material during operation of the filter device—is difficult to remove during a later cleaning process, such as CIP process. If the deposited material originates from the product it may be necessary first to dissolve the material before it can be rinsed out of the pocket. In fact, during a CIP process the aim is to first dissolve the deposited material and then rinse it out of the pocket. However, even after cleaning there may still be material left in the pocket which may form basis for bacteria growth and an increased amount of bacteria in the final product. This is mostly undesired if the filter bag is used in the food or pharmaceutical industry.
Filter bags with an unfolded filter body are known from WO 01/51172 that discloses a filter bag with an upper end having an unfolded filter body provided with an outer ring-shaped stiffener. When this filter bag is mounted in the filter device the ring-shaped stiffener rests on the upper surface of the partition wall dividing the filter device into a dust chamber and a clean-air chamber while the main body of the filter bag extends into the dust chamber. Since the forces acting on the filter bag are mainly directed from the outside to the interior of the filter bag there is a risk that the filter body is separated from the outer ring-shaped stiffener by tearing or rupturing, thus creating a gap through which dust particles can pass. Measures must therefore be taken to assure that the filter body is not unintentionally separated from the ring-shaped stiffener. In WO 01/51172 this is assured by providing an inner basket with a rigid upper ring that provides support to the inside of the filter body at the area of the ring-shaped stiffener. If no inner ring is provided the forces acting on the filter bag may cause the filter body to be separated from the ring-shaped stiffener, or the ring-shaped stiffener is forced to flex inwards, leaving a gap between the opening in the partition wall and the filter bag. Another disadvantage of the filter device shown in WO 01/51172 is that the small crevice between the upper surface of the partition wall and the ring-shaped stiffener is difficult to clean thoroughly which, again, is mostly undesired especially if the filter device is used in the food or pharmaceutical industry.
It is an object of the present invention to provide a filter bag and a filter device that overcomes the problems associated with the prior art filter bag and filter device.